During engine non-fueling conditions in which at least one intake valve and one exhaust valve are operating, such as deceleration fuel shut off (DFSO), ambient air may flow through engine cylinders and into the exhaust system. In some examples, an exhaust gas sensor may be utilized to determine ambient humidity during the engine non-fueling conditions. However, the need to wait for a DFSO condition can delay the humidity measurement. In addition, it may take a long time for the exhaust flow to be devoid of hydrocarbons during the engine non-fueling conditions. Further, during the DFSO, when an intake throttle is closed, large manifold vacuum is generated which can lead to ingestion of a large amount of PCV. The ingested PCV can impact the sensor output and confound the humidity measurement. Overall, an accurate indication of ambient humidity may be delayed.
The inventors herein have recognized the above issue and have devised an approach to at least partially address it. Thus, a method for an engine system which includes an exhaust gas sensor is disclosed. In one example, the method comprises: selectively deactivating a first group of cylinders while maintaining a second group of cylinders active, modulating a reference voltage of a first exhaust gas sensor coupled downstream of the first group of cylinders, inferring an ambient humidity based on sensor output generated by the first sensor responsive to the modulating; and adjusting an engine operating parameter of the second group of cylinders based on the inferred ambient humidity. In this way, the humidity estimation may be performed in the deactivated bank of a variable displacement engine, reducing the need to wait for a DFSO condition.
As an example, during low load conditions, cylinders on a first engine bank may be selectively deactivated while cylinders on a second engine bank remain active. This reduces pumping losses and improves engine efficiency. While fuel and spark to the first engine bank is deactivated, a first exhaust gas oxygen sensor coupled downstream of the first engine bank (but not the second engine bank) may be modulated for ambient humidity detection. Specifically, each of a first, lower voltage (e.g., 450 mV) and a second, higher voltage (e.g., 1080 mV) may be alternately applied on the sensor and a sensor output each voltage (e.g., a pumping current at each voltage) may be noted. Based on a difference between the first and second pumping currents, an ambient humidity may be estimated. Concurrently, while the second engine bank is active, a second exhaust gas oxygen sensor coupled downstream of the second engine bank (but not the second engine bank) may be modulated for fuel ethanol content detection and/or exhaust air-fuel ratio determination. Specifically, during a first condition, only the first voltage may be applied on the second sensor and an air-fuel ratio may be estimated based on a first pumping current output by the sensor. Then, during a second condition, each of the first and second voltage may be alternately applied on the second sensor and fuel ethanol content may be estimated based on a difference between the first and second pumping currents output by the sensor at the first and second voltages, respectively. An engine operating parameter of the active bank (e.g., fuel injection amount, spark timing, EGR amount, etc.) may then be adjusted based on the ambient humidity estimated on the inactive bank, as well as the air-fuel ratio and ethanol content estimated on the active bank.
In this way, by modulating the reference voltage and determining the change in pumping current at an exhaust gas oxygen sensor coupled to a selectively deactivated engine bank, the need to wait for a DFSO condition is reduced while also nullifying the effect of any changing air fuel ratio. By not waiting for a DFSO condition, the PCV impact on humidity estimation is also reduced. Further, the ambient humidity may be determined in a shorter amount of time, as the exhaust air fuel ratio does not have to be stable before an accurate indication of ambient humidity may be determined. Further still, by concurrently modulating the reference voltage and determining the change in pumping current at an exhaust gas oxygen sensor coupled to the active engine bank, fuel ethanol content estimation and air-fuel ratio estimation can be performed at the same time as ambient humidity estimation.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.